Conventionally, metallic pigments have been used for metallic coatings and printing inks, for kneading into plastic, and the like for the purpose of achieving a decorative effect with a focus on metallic feeling.
Recently, in the field of coatings, in view of resource saving and anti-pollution, there has been an increasing need for conversion to water-based coatings in which the amount of an organic solvent used is small, but there are still few examples of water-based coatings which are practicable in metallic coatings containing a metallic pigment. The reason for this is that metallic pigments are easily corroded in water-based coatings. In the case where metal powders are present in water-based coatings, the metal powders are corroded by water in an acidic, neutral or basic region, or in multiple regions of them depending on the nature of each metal, thereby generating a hydrogen gas. This is an extremely serious safety problem during production processes of coatings and inks in paint manufacturers and ink manufacturers as well as during processes of coatings and prints in automobile manufacturers, home appliance manufacturers and printing companies. The corrosion resistance of metallic pigments in water, water-based coatings or water-based inks is, hereinafter, referred to as “storage stability”.
Patent Document 1 discloses an aluminum pigment having an inorganic molybdenum coating film, and also a coating film made of amorphous silica, which covers the inorganic molybdenum coating film.
In addition, Patent Document 2 discloses an aluminum pigment having an inorganic molybdenum coating film and also a coating film made of amorphous silica and/or a coating film formed from a silane coupling agent, which covers the inorganic molybdenum coating film.
However, in any of these patent documents, the deterioration in color tone of the metallic pigment is not avoidable, and the processes therein are also complicated.
In order to simultaneously achieve storage stability in water-based coatings or water-based inks and the maintenance of the color tone of a metallic pigment in them, Patent Document 3 discloses a metallic pigment containing an amine salt of molybdic acid and Patent Document 4 discloses a metallic pigment containing an amine salt of heteropoly acid.
However, in any of these patent documents, storage stability is insufficient. In addition, in any of these patent documents, there is a disadvantage that a dye or an organic pigment in coatings is partially discolored in the case where it is blended with the coatings. Furthermore, in some applications, a coating film obtained by using the metallic pigment is often required to have adhesion and chemical resistance such as acid resistance or alkali resistance.